Fields and clearings, roadsides, dry banks and hillsides, rocky slopes and summits, in open ground or open forests.

Notorious for hybridizing with R. typhina; presumed hybrids (R. ×pulvinata Greene) are more common in Michigan than pure R. glabra, and perhaps have a slightly wider distribution. The hybrids, and both parents, form large, uniform colonies from root suckers.

Hybrid variants may be conveniently sorted into the following four groups:

(1) New branches and petioles with dense hairs but few if any as long as in R. typhina; fruit (if present) with hairs shorter than in R. typhina, ± blunt or some of them clavate.

(2) New branches and petioles glabrous or nearly so but fruit with the characteristic long sharp-pointed hairs of R. typhina. [Vegetative or staminate specimens of such a variant would probably be referred to R. glabra by most observers].

(3) Hairs of fruit partly clavate and partly sharp-pointed, shorter than in R. typhina but often a bit long for R. glabra; pubescence of vegetative parts ranging from dense and long as in R. typhina to glabrous. These are among the commonest of the presumed hybrids, and the intermediate nature of the fruit pubescence is the most convincing evidence.

(4) Hairs of fruit as in R. glabra but pubescence of vegetative parts too abundant or long for that species. Such plants seem rare.